The present invention relates to a process for utilizing light radiation with the aid of fluorescent optical fibres, as well as to functional devices and apparatus using said process and deals in general terms with technology using optical fibres. The latter has now been known for over a decade. Use is made of optical fibres, initially produced from glass but then from different plastics materials, for conducting a light signal, introduced e.g. with the aid of a focussing optics through one end of the fibre, along said fibre to its other end.
For this purpose the fibre core made from glass or a transparent plastics material is coated with a first peripheral, transparent, optical sheath having a lower refractive index than that of the material used for producing the fibre core, so that the interface between the core and the sheath is the seat of total light reflection phenomena, thus permitting the transmission of the light along said sheath without any significant loss.
The optical fibres used in this way consequently require focussing towards one of their ends of the light signal to be transmitted, as well as a very precise geometrical positioning of said ends with respect to the optical focussing means. These constraints must be respected, because in the case of such applications, it is a question of transmitting optical informations, e.g. with a view to their subsequent processing for the purposes of intelligible communications, or for the display on display screens. This is only mentioned here for information purposes, because the present invention relates to applications completely outside that of optical light fibres with a terminal digital light information input.
Moreover, for several years, so-called scintillating optical fibres have been produced, generally from plastics material and whose core is doped with the aid of appropriate products, so that the fibre material, excited by a flux of elementary particles, isotropically retransmits or reemits into the material radiation with a wavelength .lambda. exceeding .lambda..sub.1. Part of this radiation .lambda..sub.2 is lost, but a by no means negligible proportion is trapped within the fibre and is propagated by internal reflection up to the ends of the scintillating fibre, where it is collected.
These fibres are intended for use in corpuscular physics in equipment for the detection of elementary particles and for measuring parameters linked with these particles.
In particular, a very recent apparatus is known which has scintillating plates excited by a corpuscular radiation perpendicular to said plates. On their lateral edges, said plates supply the collected light signals. These lateral edges are joined to lateral scintillating fibres, which in turn supply new light signals at their ends.
The present invention has a certain analogy with this very special type of use of scintillating optical fibres, because it is based on the finding that it is possible to laterally excite a doped optical fibre, from which the mechanical protective sheath has obviously been removed, by a radiation not only of elementary physical particles as in the case of the aforementioned apparatus, but more generally by a diffuse light radiation. Thus, it essentially differs therefrom by this type of light radiation used and consequently, as will be shown hereinafter, by the sought applications and the realizations which are consequently proposed.
Among the fibres which can be used as scintillating fibres, i.e. which can be excited by corpuscular radiation, so-called fluorescent fibres are known and a number of types thereof will be described hereinafter. They are sensitive to light radiation and more specifically also to corpuscular radiation. Hitherto they have only been used in the aforementioned equipment for the detection and measurement of quantities of physical particles.
The invention uses such laterally excited fluorescent fibres, but in interaction with light radiation in a number of novel ways.